Abstract
Design of industrial scale packed bed reactors can be aided by using computational fluid dynamics (CFD)-discrete element method (DEM) simulation for understanding the transport phenomena. However, conducting CFD-DEM simulation for the whole large-scale packed bed reactor is computationally prohibitive, which limits the usage of this tool. Hence, a methodology has been developed to identify the segments of the bed, which can serve as a good representative for the CFD simulation of large industrial scale packed bed reactors. Two segments, a cylindrical cut-segment and a wall-segment, have been used to represent the core central region of packed bed and the near wall region of packed bed, respectively. The methodology determines the size (diameter and height) of the cylindrical bed cut-segment that can be a good representative for the large-scale packed bed reactor. The segments are then used to obtain the information on transport phenomena (friction factor coefficients (pressure drop) and the heat transfer/mass-transfer coefficients) for packed beds made of spherical particles and non-spherical particles. CFD simulations have been conducted on the DEM generated packing segments for a wide particle Reynolds number range (from laminar to turbulent regime) to develop the correlations. The proposed methodology (on cut-segment and wall-segment) has been validated for spherical particle packed bed by comparing results to well-established correlations (such as Ergun equation for pressure drop, Wakao correlation and multiparticle Ranz–Marshal correlation for particle heat transfer coefficient, and Dixon–Lubua and Colledge–Paterson correlation for wall heat transfer coefficient). The methodology is then applied to understand the transport phenomena and to develop correlations for long cylindrical pellet (aspect ratio 7) and fluted-ring. The pressure drop correlation obtained for the long cylindrical pellet (aspect ratio of 7) packed bed has been compared to the correlation for cylindrical pellet with aspect ratio of 5.77 (obtained by Nemec; Nemec, D.; Levec, J. Chem. Eng. Sci. 2005, 60, 6947). The comparison shows that the effect of increasing aspect ratio on pressure drop is captured as per the expected trend. The methodology has been applied in a chemical looping combustion reactor based on the pressure drop and heat transfer results. Thus, the proposed CFD-DEM methodology offers a computationally efficient way of understanding the transport phenomena in an industrial scale reactor through simulating a methodically selected segment inside the reactor. This enables design and performance assessment of such reactors.
